Antenna system



' J. w. TILEY- ANTENNA SYSTEM Dec. I 24, 1946.

Filed Jan. 29, 1945 INVENTOR.

Patented Dec. 24, 1946 ANTENNA SYSTEM John W. Tiley, Philadelphia, Pa., assignor to Phil co Corporation, a corporation of Pennsylvania Application January 29, 1945, Serial No. 575,020-

8 Claims.

acteristics and, in fact, it frequently occurs that rotation of said beam over a desired angular range is highly desirable.

The customary manner or obtaining a directional characteristic in an antenna system is to provide an antenna arrangement with a reflector, or reflectors so related to the antenna that interference patterns tend to eliminate radiation in undesired directions. Such antenna arrangements are relatively complex, require careful tuning and are difiicult to move or rotate. At high frequencies, the problem of providing sliding connections and maintaining matching and phase adjustment is diflicult. In the case of antenna systems using metal reflectors, unless a high ratio of reflector dimension-t wavelength is maintained, it is found that a sharp beam is difilcult to obtain.

By virtue of the invention hereinafter described, it is possible to obtain a controllable directional characteristic without recourse to complicated mechanism or critical electrical parts. The invention makes it possible to utilize a conventional antenna system having a more or less uniform radiation pattern without undue complexity. In general, the invention takes advantage of the phenomenon of reflection by dielectric materials to control the directional characteristic of an antenna system;

The invention in general provides for a variation in transmission path of radiation by changing the effective length of such paths through the interposition of members of dielectric material. By having a predetermined spacing between the dielectric members, it is possible to obtain a selective transmission of energy. In its more specific form, the invention provides for at least two dielectric members having a variable spacing therebetween in respect to a particular direction of transmission so that energy may be transmitted in said direction at one time and suppressed at another time. In its more practical form, t-he invention is restricted to ultrahigh frequencies where the wavelength involved is of constant thickness.

' around cable 12.

' 2 of dimensioning parts to within a substantial portion of a Wavelength,

Referring now to the drawing,

Figure 1 shows an elevation view, partly in cross section, of a system embodying this in vention.

Figure 1a is a detail showing the structure of Figure l modified.

Figure 2 is a sectional view on line 2--2 of Figure 1.

Figure 3 is a sectional view of a modified structure. 3

Figure 4 is a view of an enlarged portion of Figure 1.

Referring to Figures 1 and 2, platform or base It may be provided forsupporting the entire mechanism. Base H] may have centrally disposed apertured well ll supporting any kind of antenna system [2. As shown here by way of example, antenna system l2 comprises a coaxial line having central conductor !3 and outer conductor Hi. At various regions along the length of outer conductor I4, abay of antenna units may be provided. Thus one bay of such units may consist of arcuate electrodes 2!) supported on fingers 2| rigidly mounted at one point of outer conductor [4. Outer conductor M is apertured at 22 so that finger 2| may extend to the inside surface of outer conductor I4. Arcuate electrode 25 may be carried by finger 26 passing through aperture 22 and rigidly joined to central conductor l3. By proper choice of dimensions, electrodes 20 and 25 may form a dipole fed from within coaxial cable l2. In place of a coaxial cable, outer conductor [4 may be a wave guide with finger 26 terminating in a pick-up p within the guide.

Such a type of dipole is generally provided in a series of two or more units uniformly disposed As shown here, three sets of dipoles are provided with equal angular spacing around the cable. extending vertically, will provide a generally uniform horizontal pattern. By providing a series of superposed antenna bays, a desirable pattern may be obtained. It is understood of course that the proper vertical spacing between adjacent antenna bays is important so that radiation will be in phase. Inasmuch as such antenna. systems are well known, a detailed description and discussion of such an antenna system is unnecessary.

In order to control the radiation pattern, outer dielectric member 34 is provided. As shown here, member 34 is a circular cylinder of substantially If different efiectsare de- Such an antenna array, if.

sired then member 34 may have other shapes. Cylinder 34 may be supported on base It] in any suitable fashion, and, in this particular instance, is preferably disposed concentric with the electrical center of the antenna system. Inasmuch as the antenna system here is symmetrical in horizontal planes (a, vertical disposition of the antenna is assumed), the electrical. center of the antenna system is substantially coincident with the geometrical center of coaxial cable l2. Thus horizontal radiation patterns of the antenna system, if disposed in free air, would be circular with respect to the axis of the coaxial cable.

Referring to Figure 42, the axis of cylinder 34 is indicated at 35. Eccentric with respect to axis 35 is inner dielectric member 38 which, for convenience, may also be a circular cylinder having axis 37. Both cylinders are preferably constructed of dielectric material having low transmission losses for radiant energy such as polystyrene or quartz. The thickness of cylinders 34. and 36 should preferably be uniform, and small with respect to the wavelength employed, that is, considerably less than a quarter wavelength.

Cylinder 36 i rotatably mounted upon turntable it carried by thrust bearing 4!. Turntable All may have its peripheral portion formed as a gear and may be driven by worm 42. As shown in Figure 1, cylinder 34 is carried upon base it. It is also possible to rotate both cylinders 34 and 36 by mounting them upon turn-table 40' as shown in Figure 1a. Thus in both figures, as the turn-table rotates, the direction of maximum and minimum cylinder separation will'also rotate.

It will be apparent that the portions of wall 36 on the opposite sides of axis 35 are displaced differently therefrom. For maximum directional effect, the spacing between walls 35 and 3,4 in one direction should be a quarterv wavelength, and on the opposite side of axis 35, the spacing between walls 3:1 and 35 should be a half wavelength. Under these conditions, waves will propagate freely in the direction where the spacing is a quarter wavelengtha ld willbe substantially entirely reflected. in the, direction, when the Spac ing is a halt wavelength. The impedance of. the antenna input terminals and the, degree of directivity of the antenna system may be adjusted by varying the spacings ShOWn' in Figure. 4 and the thickness of, the dielectric. cylinders, but as these factors may be, calculated. by methodswell known to those skilled in the art it is unnecessary to describe them here in detail. However, an improved application of my invention which would not be evident from calculation is shown in Figure 3.

Figure 3 illustrates the case where an, antenna system similar to that shown in Figuresl and 2 Cylinder 36 to cylinder 34; one-quarter" wavelength Cylinder 3 2 to cylinder it, three-quarter wavelength Cylinder 46 to cylinder 34, one-quarter wavelength. 7

The addition of cylinders i l and 45 will enhance the directive properties of the antenna system of Figures 1 and 2 without afiecting the impedance at the antenna terminals to any marked extent.

If it is desired to rotate the direction of wave emission, a structure similar to. that of Figure 1 may bejus'ed, the platform, w being made large enough to accommodate the bases of all the cylinders except the outermost one. Cylinder 34, being mounted concentrically may be rotated Without effect on its operation, and eccentrically disposed cylinders 35 and 43 are suitably located on the rotating platform st.

It is understood that the drawing does not show the parts in proper proportion. Thus, the diameter of the outermost portions of the antenna system proper in practice would be smaller in proportion to the cylinder diameters than is actually shown. The smaller the diameter of the antenna proper compared to the dielectric cylinders and the smaller the thickness ness along the path of radiation of less than a quarter wavelength, a second dielectric member interposed between said antenna and said first dielectric member, said second member having a thickness of less than a quarter wavelength, and means for varying the distance between said dielectric members, said variation being sufficiently great so that said two dielectric members cooperate to transmit radiation from the antenna. in one position and to substantially suppress radiation in another position.

2. A directional antenna system according to claim 1 wherein the spacing between said dielectric members in one direction is an odd number of quarter wavelengths, and in another direction is an even number of quarter wavelengths.

3. A directional antenna system according to claim 1 wherein the spacing between said dielectric members in one direction is an odd number of quarter wavelengths and wherein said spacing in the opposite direction is an even number of quarter wavelengths.

4. A directional antenna system according to claim 1 wherein said dielectric members are cyl-,

inders and dimensioned so that the spacing between said cylinders in one direction is an odd number of quarter wavelengths and in the opposite direction is an even number of quarter Wavelengths.

5. A directional antenna system comprising an antenna having a radiation pattern in a predetermined plane, a plurality of pairs of dielectric members disposed in the path of said radiation from said antenna system, each dielectric member having a thickness along the path of radiation, of less than a quarter wavelength, means for varying the distance between the dielectric members forming each pair, said variation being suificiently great so that the dielectric members forming each pair cooperate to transmit radiation from the antenna. in one direction and to substantially suppress radiation in another direction.

6. The system of claim 5 wherein said dielec- 6 mounted on a turntable, said turntable being adapted to turn said cylinder and vary said direction.

8. The system of claim 5 wherein all but the outermost of said cylinders are mounted on a turntable, with one of each pair of cylinders being mounted concentric to said turntable and with the remaining cylinders being mounted eccentric to said turntable but having a common 10 center.

JOHN W. TILEY. 

